Photogrammetry is the practice of determining the geometric properties of objects from photographic images. In the simplest example, the distance between two points that lie on a plane parallel to the photographic image plane can be determined by measuring their distance on the image, if the scale s of the image is known. This is done by multiplying the measured distance by 1/s.
A more sophisticated technique, called stereo photogrammetry, involves estimating the three-dimensional coordinates of points on an object. These are determined by measurements made in two or more photographic images taken from different positions (see stereoscopy). Common points are identified on each image. A line of sight (or ray) can be constructed from the camera location to the point on the object. It is the intersection of these rays (triangulation) that determines the three-dimensional location of the point. More sophisticated algorithms can exploit other information about the scene that is known a priori, for example symmetries, in some cases allowing reconstructions of 3-D coordinates from only one camera position.
There are known current shortcomings of the available solutions. Indeed, the optimal solution was to use a bundle adjustment which is computationally expensive due to the fact that all data is required before the solution can be computed. This means a bundle adjustment per se is not appropriate for real-time implementation.
Alternative solutions include the usage of a Kalman filter. However, this approach fails to take advantage of the connection of the current measurements to previously estimated position and orientation states.
A third solution is to use pairs or triplets of images to estimate the relative motion between the frames. This solution suffers from drift due to the loss of information connecting the measurements to images outside the pair/triplet used for the estimation.